I am about to fix a external upvc cill & window for my garage window.I have read that you can either cement cill into place or use a few beads of mastic ,which seems a better idea.
Any ideas as to what you can use ? would it be something like gripfill,no nails, silicon or something similar which would set hard after a while.

I have over the years just used silicone sealant purchased from local store,now closed after 27 years to re-seal around my house upvc windows .I decided to see what if any silicone sealant is superior.As mentioned somewhere on forum the Low Modulus Silicone Neutral Cure seems to be best as it sticks to brickwork & frame better.
However they do say it is dearer than normal High Modulus silicon.Had a look in the Wicks book but no mention of if any of their silicone sealants are high or low and indeed if any one is suited for upvc windows.
I then went to the Screwfix web page and they do sell a Low Modulus Silicone but at only £2.69 a tube.That has thrown me a bit.Has anyone used this Screwfix silicone or recommend a silicone from either shed that would be suitable but good.
Thank you

Low modulus also goes by the title of 'neutral cure'. Haven't used the screwfix one. I tend to use Arbo, but i would personally use a good named brand if poss. Some of the cheaper silicones are a bit ......... well let's say you get what you pay for. That's just my opinion

To fit a upvc window
Turn the window upside down you can use high mod or low mod silicone.
Bed the cill to the frame using silicone on the back edge of the frame and screw the cill to the frame to hold in place.
Dont go mad with the silicone just the back of the cill.
Low modular silicone is best to seal the frame to the brickwork,High mod is best for plastic to plastic.

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